The present invention relates to an image recording apparatus for recording information such as images, characters or the like on a recording medium and more particularly to an image recording apparatus for recording information such as color images characters or the like using toner of K (black), C (cyan), M (magenta) and Y (yellow) colors.
Various kinds of known image recording apparatus are designed to obtain images on image receiving materials by the use of colored material sheets having colored material layers capable of heat transfer by heating the colored material sheets according to imaging patterns so as to transfer the heated or non-heated portions of the colored material layers to image receiving layers. More specifically, a colored material sheet with a hot-melt, thermal adhesive or sublimational colored material layer formed on a substrate is used for forming a latent image on a colored material layer by heating the colored material layer according to an imaging pattern with optical beams such as laser light from the back side of the colored material sheet (what is opposite to the colored material layer) or the back side of an image receiving material at least in a recording position by stacking the colored material sheet and the image receiving material in order to make the colored material layer and the image receiving material sufficiently adhere to each other. Then the exposed portion of the colored material layer is transferred onto the image receiving layer so as to transfer the image onto the image receiving material by peeling the colored material sheet off the image receiving material.
FIG. 8 is a schematic diagram of such a related image recording apparatus as aforesaid. FIG. 8(a) shows an example of an outer drum type in which the surface 24a, which is coated with a colored material, of a recording medium 24 is arranged on the outer side of a recording drum 23 by putting the coated surface 24a face up so that the coated surface is irradiated with laser light emitted from an optical head 21 for heating from the outside; FIG. 8(b), an example of an inner drum type in which the coated surface 24a of a recording medium 24 is arranged on the inner side of a recording drum 23b by putting the coated surface 24a face up so that the coated surface 24a is irradiated with laser light for heating from the outside; and FIG. 8(c), an example of an inner drum type in which the coated surface 24a of a recording medium 24 is arranged on the outer side of a transparent recording drum 23c by putting the coated surface face down so that the coated surface 24a is irradiated with laser light for heating from the inside of the recording drum 23c. 
These three examples are of such a type that the coated surface is directly irradiated with laser light. In other words, any problem of polarization dependence does not develop in the substrate of the recording medium when image recording of this type is carried out.
In the case of a heat transfer type image recording apparatus as shown in FIG. 9, on the other hand, a recording material 24 prepared by laying a toner layer 24a coated on a transparent substrate 24b of a toner sheet on top of the image receiving layer of an image receiving sheet is arranged on the outer side of a recording drum 23 by putting the transparent substrate 24b of the toner sheet face up and the toner-coated surface 24a is irradiated with laser light for heating from and through the substrate 24b. 
In the example of the related heat transfer type image recording apparatus, a PET (polyethylene terephthalate) base, a TAC (triacetyl cellulose) base and a PEN (polyethylene naphthalate) base for use as the substrate of the toner sheet are made into a film having uniform thickness by the orientation method.
However, moleculars are orientated in one direction because these materials are forced to stretch out at the time of the orientation, thus causing polarizing characteristics. In the case of FIG. 9, the following problems still exist: since the colored material sheet is heated after the laser light is passed through the PET base, the transmissivity and the reflectivity vary when polarized light such as laser light is incident on the polarization-dependent PET base and when the polarizing direction of the laser light differs from that of the PET base and therefore the recording sensitivity is lowered at an angle at which the transmissivity becomes reduced and nonuniformity of images occurs when the transmissivity has an in-plane distribution.
It is therefore an object of the present invention to provide an image recording apparatus for use in increasing recording sensitivity by adjusting polarizing directions of a substrate of the toner sheet and recording laser light so that the polarizing directions of the substrate of the toner sheet and the recording laser light are brought into coincidence with each other, decreasing light energy to be consumed wastefully in the substrate of the toner sheet by transmitting laser power through the substrate up to a photothermal conversion layer as much as possible so as to convert the light energy into thermal energy, and for making use of energy effectively by decreasing the quantity of light reflected from the substrate of the toner sheet.
In order to achieve the above object, there is provided an image recording apparatus for recording an image on a recording medium, which comprises a transparent substrate having dependence on polarization and a photosensitive layer provided on the substrate, by providing light energy of polarized light transmitted through the substrate into the photosensitive layer, comprising a laser light source emitting laser light as the polarized light, the polarizing direction of the laser light is made coincident with the polarizing direction of the substrate.
Specifically, an angle made by the polarizing direction of the substrate and the polarizing direction of the laser light is xc2x130 degrees or smaller.
Accordingly, the polarizing directions of the substrate and the laser light are set parallel to each other, which results in increasing the transmissivity and decreasing the quantity of attenuation of the laser light, whereby recording sensitivity is enhanced.
It may be configured that: an optical axis of the incident laser light is tilted with respect to a normal of the substrate.
The tilted angle between the normal of the substrate and the optical axis of the laser light may be proximate to the Brewster""s angle of the substrate.
The tilted angle between the normal of the substrate and the optical axis of the laser light may be in the range of 1-65 degrees.
According to the above configurations, the transmissivity can be further improved.
It may be configured that: the recording medium is a photo-heat-sensitive transfer material including a transparent substrate and a photo-heat-sensitive transfer layer.
According to the present invention there is also provided an image recording apparatus for recording an image on a recording medium, which comprises a transparent substrate having dependence on polarization and a photosensitive layer provided on the substrate, by providing light energy of polarized light transmitted through the substrate into the photosensitive layer, comprising: a rotary drum on which the recording medium is mounted; and a laser head emitting laser light as the polarized light, the polarizing direction of the laser light is made coincident with the polarizing direction of the substrate.
Accordingly, the polarizing directions of the substrate and the laser light are set parallel to each other, which results in increasing the transmissivity and decreasing the quantity of attenuation of the laser light, whereby recording sensitivity is enhanced.
It may be configured that: an optical axis of the incident laser light is tilted with respect to a normal of the substrate.
Accordingly, the transmissivity can be further improved.
It may be configured that: the recording medium is a toner sheet roll, in which the polarizing direction of the substrate is coincident with an axial direction thereof, to be disposed into the image recording apparatus, and the polarizing direction of the laser head is oriented to an axial direction of the rotary drum.
Accordingly, lacking in image uniformity can be obviated by making compensating for mainly the lateral polarizing direction of the substrate of the toner sheet in the image recording apparatus.
It may be configured that: the recording medium is a toner sheet roll, in which the polarizing direction of the substrate is coincident with a circumferencial direction thereof, to be disposed into the image recording apparatus, wherein the polarizing direction of the laser head is oriented to a rotational direction of the rotary drum.
Accordingly, lacking in image uniformity can be obviated by making compensating for mainly the vertical polarizing direction of the substrate of the toner sheet in the image recording apparatus.
It may be configured that: the laser head is configured so as to be rotatable around an optical axis of the laser light emitted therefrom.
It may be configured that: the image recording apparatus further comprises a phase plate rotatably provided at one of an emission side and inside of the laser head.
Accordingly, the polarizing direction of the laser light can be simply changed by rotating the laser light head or the phase plate with respect to the optical axis.
It may be configured that: information for indicating the polarizing direction of the substrate is recorded at least one of the recording medium and a package of the recording medium.
Accordingly, troublesome of measuring the polarizing direction of the toner sheet for use each time can be saved and the image recording apparatus becomes user-friendly.
The indicating information is constituted by at least one of a numerical value, a symbol, a bar code, a magnetic recording medium and an IC card.
It may be configured that: the image recording apparatus further comprises: a reading device for reading the indicating information; and a driving device for rotating the laser head around an optical axis of the laser light emitted therefrom so as to make the polarizing direction of the laser light coincident with the polarizing direction read from the indicating information by the reading device.
Alternatively, the image recording apparatus further comprises a driving device for rotating the phase plate so as to make the polarizing direction thereof coincident with the polarizing direction read from the indicating information by the reading device.
Accordingly, the user needs not to do anything in particular regarding the adjustment of the polarizing direction.
It may be configured that: the recording medium is a photo-heat-sensitive transfer material including a transparent substrate and a photo-heat sensitive transfer layer.